Self-nonself discrimination

Self-nonself discrimination is the fundamental problem that the immune system must solve: distinguishing the body's own cells and molecules ('self') from foreign pathogens and abnormal cells ('non-self'). This distinction is not given but must be learned, maintained, and continuously enforced at the molecular level.

The classical account, associated with Frank Macfarlane Burnet's clonal selection theory, holds that self-tolerance is established during development through the deletion of self-reactive lymphocytes. But this account is incomplete: autoimmune disease demonstrates that self-tolerance sometimes fails, and recent work on regulatory T-cells and peripheral tolerance shows that the boundary between self and non-self is actively maintained rather than hard-coded. The problem is not merely biological. It is formally analogous to the Byzantine generals problem in distributed systems: how does a network distinguish legitimate signals from corrupted or malicious ones when no central authority exists to verify identity?